This invention relates to bearing structures and, more particularly, to a combination plastic-metallic trolley wheel assembly incorporating a race structure which increases the life, durability, and reduces wear of the structure.
Conventional trolley wheels used in typical overhead conveyor systems in manufacturing and fabrication plants have long utilized metallic wheels with bearings supported intermediate the wheel and an inner race. Such wheels have deteriorated undesirably in many applications, especially in the food processing industry where trolley wheels on conveyors are subjected to high heat and moisture conditions, are frequently washed to maintain cleanliness, and must also bear relatively high loads.
Recently, a sanitary trolley wheel has been designed as disclosed in copending, commonly assigned United States patent application Ser. No. 528,794 entitled SANITARY ANTIFRICTION TROLLEY WHEEL, filed Dec. 2, 1974, invented by Frederick R. Sytsma. This sanitary trolley wheel assembly includes at least one metallic, annular outer race ring supported on a plastic tire or wheel and spaced from an inner race with bearings supported between the races. This assembly has been revolutionary in solving many of the problems previously encountered in the food processing industry in connection with overhead conveyors since it can bear high loads, is substantially noiseless in operation, does not flake or chip causing particles of the wheel assembly to drop onto the food being processed, and can be subjected to high heat and moisture conditions such as steam cleaning without corrosion or other deterioration. In certain applications of the wheel assembly, it has been found that the metallic outer race ring has rotated with respect to the wheel or tire during use causing wear and eventual sloppiness in the assembly. This also causes friction which produces heat buildup which also tends to shorten the life of the assembly.
An associated problem encountered in the above trolley wheel assembly as well as other bearing assemblies utilizing races of materials dissimilar from the associated tire or wheel has been the inability to efficiently and effectively retain the dissimilar races to the wheel over the life of the assembly. In one attempt, tangs or flanges on the race rings were impressed into the dissimilar material of the wheel. Such rings would eventually separate from the wheel. Further, it has been found that if the wheel material is plastic, especially the type which can bear heavy loads, the plastic tends to expel the rings and the tangs or flanges therefrom.
Accordingly, there has been a need for a trolley wheel assembly which is durable, long wearing, can be subjected to high heat and moisture conditions such as in sanitary food processing applications, which retains the benefit of a plastic tire or wheel, and yet can bear heavy loads. Especially in plastic tire and metallic outer race ring combinations, there has been a need for an assembly which avoids rotation between the race rings and the wheels and prevents separation therebetween.